Synopsis The Cessna 208B aircraft (registration C-GRXZ, serial number 208B0469) was en route at 9000 feet above sea level, from Tofino, British Columbia, to Vancouver International Airport, British Columbia, when the engine failed. The pilot began a glide in the direction of the Port Alberni Regional Airport before attempting an emergency landing on a logging road. The aircraft struck trees during a steep right-hand turn and crashed. The accident occurred at about 1420 Pacific standard time, approximately 11 nm south-southeast of the Port Alberni Regional Airport. Five passengers survived with serious injuries; the pilot and the other two passengers were fatally injured. Ce rapport est galement disponible en franais. Minister of Public Works and Government Services Canada 2007 Cat. No. TU3-5/06-1E ISBN 978-0-662-47472-2 1.0 Factual Information 1.1 History of the Flight The pilot took off from Tofino, British Columbia, at 1353 Pacific standard time1 on an instrument flight plan. The flight was over a designated mountainous region, in visual meteorological conditions (VMC)2, above broken layers of cloud. Following the engine failure, the pilot began a right turn, declared an emergency to the Vancouver Area Control Centre, British Columbia, and requested a range and bearing to the nearest airport. At this time, the aircraft's rate of turn increased, and the aircraft rolled out on a heading direct to the PortAlberni Regional Airport, BritishColumbia, about 17nautical miles (nm) to the northwest. The pilot was currently in VMC, but he would have to enter cloud during the descent. The pilot then requested navigational information to help keep the aircraft clear of the mountains. Communication with the aircraft was lost as it descended through 7000feet above sea level (asl). Radar data show that, at about 6000feet asl, the pilot entered a tight left-hand, 360 turn, during which the rate of descent increased to about 2500feet per minute. The aircraft came out of the turn at 4500feet asl on a heading toward the Port Alberni Regional Airport. Aircraft in the area heard the pilot transmit a Mayday call indicating that he was attempting a forced landing on a logging road. The aircraft struck trees during a steep right-hand turn and crashed. Although fuel leaked into the cabin after the crash, there was no fire. 1.2 Engine Examination The engine (PT6A-114A, serial number PCE19352) was removed from the wreckage and transported to an approved teardown facility. It was determined that all 58blades in the compressor turbine (CT) section were broken. The CTblades had fractured at different heights relative to their blade tips. One particular blade was fractured near the airfoil root platform, and the topography of the fracture surface showed signs of fatigue cracking. The compressor had seized because of bearing damage following the CT blade failure. 1.3 Metallurgical Examination Relevant parts of the engine were examined at the TSB Engineering Laboratory. Conclusions based on that examination are as follows: One CT blade failed as a result of the overstress extension of a fatigue-generated crack. The fracture initiated at a metallurgical anomaly in the parent blade material. The fatigue crack progressed from the initiation site near the trailing edge, toward the leading edge in a high cycle mode, eventually resulting in blade failure due to overstress rupture when the remaining area could no longer support the applied loads. The remaining CT blades and the power turbine blades failed as a result of impact damage from the debris generated when the first CT blade failed. The number two bearing assembly failed as a result of the imbalance created when the CT blades broke. 1.4 Engine History The engine was manufactured in 1995 by Pratt Whitney Canada (PWC) and is assigned a basic time between overhaul (TBO) of 3600hours. The engine had been overhauled twice since new. The first overhaul was done in the UnitedStates and was completed at 3528hours. A hot section inspection was done on 22October 2003, at 7677hours, and all 58CT blades were replaced with new blades. A TBO extension to 6000 hours was requested at that time and was granted in accordance with PWC Service Bulletin (SB)1703. The second (most recent) engine overhaul was completed on 07November 2005, at 9528hours. During that overhaul, the CT blades that had been installed new in October 2003 were inspected and re-installed in accordance with approved PWC overhaul procedures. At the time of the accident, the engine had accumulated about 140hours of flight time since the most recent overhaul. The failed blade had been in operation for about 1991hours since new. 1.5 Engine Condition and Trend Monitoring The installation of an engine parameter recording system and use of an engine condition trend monitoring (ECTM) software is a condition of SB1703 and must be fulfilled before allowing an extension to the TBO. Guidelines and standards for ECTM are contained in the PWC ECTM user's guide and reference manual, and in service information letter (SIL)Gen-055. Those standards indicate that engine parameters should be recorded daily and processed in the ECTM software at least every three days. This is to ensure the quality of the recorded parameters during the downloading, and to ensure that the instrumentation that records the parameters remains functional. Sonicblue Airways was providing recorded engine parameters for processing and analysis, but on a weekly basis. A review of the recorded engine data from the accident aircraft, as well as previous archived data, showed that there had been no exceedence of engine parameters and no change in the trend values over the period since the most recent overhaul. Recorded data for the last portion of the accident flight showed that the compressor speed (Ng) indicated 0rpm, consistent with a seized compressor section, and the propeller rpm ranged between 5 and 19rpm, consistent with a feathered propeller. 1.6Commercial Single-Engine Instrument Flight Rules Operations Canadian Aviation Regulations (CARs) allow air operators to fly single-engine aircraft under instrument flight rules (IFR) providing they are authorized to do so in their air operator certificate, and providing they comply with the applicable Commercial Air Service Standards (CASS). Section723.22 of the CASS restricts single-engine instrument flight rules (SEIFR) operations to specific aircraft types, stipulates a proven mean time between failure (MTBF) for the engines that are used, establishes certain additional aircraft equipment requirements, and requires additional training for the involved pilots. Both the pilot and the aircraft met the CAR standards for SEIFR. 1.7 Engine Reliability SEIFR authorization is based, in part, on the improved reliability of turbine engines as compared to their piston-engine counterparts. An essential element for SEIFR approval is that failure rates of the involved engine must remain low. CARs require the MTBF to be less than 0.01failures per 1000hours of flight time. PWC uses industry standard methods for calculating the MTBF of its engines. A basic In Flight Shut Down (IFSD) is an IFSD that is caused by a malfunction directly related to the engine or an engine component. These events are used in MTBF calculations and include unsubstantiated events where investigations are still in progress to identify the primary part that caused the event. A non-basic IFSD is an IFSD caused by a component failure not directly related to the engine. These events are not included in the MTBF calculations and, for example, would include fuel pump failure, loss of oil pressure, bird ingestion, propeller failure, operator or maintenance error such as improper fuel load, failure to correctly complete compressor washes, engine overspeeds, engine over-temperatures, or improper engine adjustments. In 2005, the basic IFSD rate for the PT6A-114A engine was about 0.0025failures per 1000hours. However, over the same time period, the total IFSD rate for the year, considering all causes, was approximately 0.01failures per 1000hours. Other Canadian-approved flight operations such as extended range twin-engine operations (ETOPS) are also authorized, in part, because of the increased reliability of modern turbine engines. ETOPS are governed by Transport Canada's (TC) TP 6327 entitled Safety Criteria for Approval of Extended Range Twin Engine Operations (ETOPS). Appendix A of that publication recognizes that: No single parameter by itself, without other data/information, can adequately qualify reliability. There are a number of variables, maintenance and operating statistics and general information about the operational experience of a particular power unit, which characterize propulsion system reliability. 1.8 Mountainous Regions TC first permitted SEIFR operations in Canada in 1993. At that time, the associated standard prohibited such operations in designated mountainous regions. Experience since 1993 has validated the premise behind SEIFR, which was that the reliability of modern turbine engines has made engine failure a low-probability event. Additionally, recent SEIFR rules published by the United States Federal Aviation Administration and the Australian Civil Aviation Safety Authority (CASA) do not contain prohibitions for flight over mountainous terrain. TC removed the restriction to SEIFR operations in designated mountainous regions in December 2000 in response to a report from industry proposing a need for changes to the regulations and standards governing SEIFR. 1.9 Navigation Equipment In the event that an emergency landing is required, Section723.22 of the CASS requires that an aircraft used in SEIFR operations have an electronic means of rapidly determining the location of the nearest airport and navigating to it. For an operator to be assured that such equipment is able to perform accurately, it must not only be functioning (serviceable), but the data it is using to calculate the exact whereabouts of the nearest suitable airfield must be accurate. This requirement can only be met through the use of the most current databases available. The accident aircraft was equipped with an approved King KLN 89B global positioning system (GPS) navigation system, but the system had an expired aviation database that was more than seven years out of date. A button on the King KLN 89B GPS allows the pilot to display the range and bearing to the nearest airports; with the exception of the age of the database, this equipment meets the requirements of Section723.22 of the CASS. Although not currently required by regulation, more modern GPS equipment is available that provides moving map displays, obstacle information, as well as the positions of towns, cities, roads, or other geographical features that could potentially be used to identify emergency landing sites if there are no airports within gliding range. 1.10 Terrain Awareness Equipment The air traffic control system in Canada does not have detailed low-level terrain information; therefore, a controller has no ability to provide obstacle clearance information to a pilot. However, modern aircraft systems that display this type of information are available. These include enhanced ground proximity warning systems (EGPWS), and terrain awareness and warning systems (TAWS). At the time of the accident, Canada had no requirement for terrain avoidance equipment to be installed on aircraft engaged in SEIFR operations. Unlike the Canadian regulations, Section 135.154 of the United States Federal Aviation Regulations does not allow the operation of a turbine-powered airplane configured with six to nine passenger seats, excluding any pilot seat, unless that airplane is equipped with an approved terrain awareness and warning system that meets as a minimum the requirements for ClassB equipment in Technical Standard Order (TSO)-C151. 1.11 Aircraft Glide Performance A graph in the Cessna 208B pilot operating manual shows that an aircraft equipped with a cargo pod should be able to glide about 2nm for every 1000feet of altitude loss in glide configuration. In this accident, the aircraft was 9000feet asl when the engine power was lost. The nearest airport was at PortAlberni, about 17nm to the northwest, at an elevation of 247feet asl. Calculations indicate that, based on the published glide ratio, and given the weather conditions at the time of the accident, it would have been theoretically possible for the aircraft to glide to the PortAlberni Regional Airport and have sufficient altitude while descending to overfly all of the en route terrain obstacles on the direct track line. This scenario presupposes that the glide path be immediately established after the engine failure, awareness that there were no en route terrain obstacles, and a preparedness to enter instrument meteorological conditions (IMC). 1.12 Route/Altitude Selection The accident flight was being conducted on published low-level airways between Tofino and Vancouver. Low-level airways are not designed to take into account the proximity of various en route airports. There is no specific requirement for operators who are authorized to conduct SEIFR flights to evaluate or alter their routes to minimize the risk exposure of passengers in the event of an engine failure while en route. 1.13 Weather The Environment Canada graphical area forecast (GFA) showed that, throughout the area of the flight, there would be patchy ceilings between 800feet above ground level (agl) and 1500feet agl with broken layers above, between 2000feet and 8000feet. Ceiling heights were not reported for the PortAlberni Regional Airport. 1.14 Pilot Information In the early 1990s, TC evaluated ways to mitigate risks associated with proposed SEIFR operations.3 Part of that evaluation recognized a requirement for enhanced pilot training in preparation for SEIFR operations and concluded that pilots were to receive initial and recurrent training on engine failure in IMC. The CARs require additional pilot training in preparation for SEIFR operations. The requirements are listed in Subsection723.98(24) of the CASS, and include ground and simulator training for loss of engine power, as well as proper checklist use. Simulator and emergency training for Cessna 208B pilots working for Sonicblue Airways was accomplished through an approved course at Flight Safety International in Wichita, Kansas, UnitedStates. Flight Safety International's standard simulator training does not include either ground briefing or practice of forced landing procedures in mountainous regions under instrument flight conditions. Flight Safety International can develop and provide specialized training to meet a customer's training requirements. The pilot of the accident aircraft was qualified and met the currency, recency and training requirements of the CARs and of the company operations manual. He held a valid commercial pilot licence, a Category1 medical, a valid pilot proficiency check (PPC), and a Group1 instrument rating. He had 2480hours of total flight experience, of which about 750 had been flown in the Cessna Caravan aircraft type. Training required by Subsection723.98(24) of the CASS had been completed in February2005 at Flight Safety International in Wichita, Kansas. Autopsy and toxicology examinations following the accident found no irregularities that would have affected the accident sequence. The pilot's workload and schedule were appropriate from the perspective of both rest and duty time requirements. 1.15 Forced Landing Procedures Forced landing patterns are taught as visual manoeuvres during training for private and commercial pilot licences. There are no additional requirements for pilots to train for the completion of a forced landing pattern in instrument conditions. In this accident, based on radar and voice data, the aircraft did break out into visual conditions in time to set up for an emergency landing. 1.16 Survivability The Cessna 208B Caravan has many designed crashworthy features, including 14g seats at all positions, shoulder belts for all occupants, and a reinforced keel along the fuselage bottom. Cessna has also designed the main landing gear to absorb the initial shock of a forced landing. In this occurrence, the seat frames buckled from the excess gloading, but all harnesses held. The aircraft's two fuel shutoff valves, one in each wing root, were found with one in the fully open position, and one in a partially open position. Part of the forced landing check requires the pilot to close the fuel valves before touchdown. It is not known whether the pilot completed this checklist item. During the impact sequence, both wing support structures were damaged. Any fore-aft movement of the wing could also have caused the fuel valve actuating cable to move from its selected position. Regardless, the design of these fuel valves is such that deceleration forces associated with a crash will tend to move the valves toward the OPEN (forward) position. In this occurrence, fuel did leak into the cabin area, causing some chemical injury to one passenger and increasing the risk of a post-crash fire.